Piezoelectric effect and electroactive phase nucleation in self-standing films of unpoled PVDF nanocomposite films

Novel polymer-based piezoelectric nanocomposites with enhanced electromechanical properties open new opportunities for the development of wearable energy harvesters and sensors. This paper investigates how the dissolution of different types of hexahydrate metal salts affects β-phase content and piezoelectric response (d33) at nano-and macroscales of polyvinylidene fluoride (PVDF) nanocomposite films. The strongest enhancement of the piezoresponse is observed in PVDF nanocomposites processed with Mg(NO3)2·6H2O. The increased piezoresponse is attributed to the synergistic effect of the dipole moment associated with the nucleation of the electroactive phase and with the electrostatic interaction between the CF2group of PVDF and the dissolved salt through hydrogen bonding. The combination of nanofillers like graphene nanoplatelets or zinc oxide nanorods with the hexahydrate salt dissolution in PVDF results in a dramatic reduction of d33, because the nanofiller assumes a competitive role with respect to H-bond formation between PVDF and the dissolved metal salt. The measured peak value of d33reaches the local value of 13.49 pm/V, with an average of 8.88 pm/V over an area of 1 cm2. The proposed selection of metal salt enables low-cost production of piezoelectric PVDF nanocomposite films, without electrical poling or mechanical stretching, offering new opportunities for the development of devices for energy harvesting and wearable sensors

Density Functional Theory and Molecular Dynamics Studies on Energetics and Kinetics for Electro-Active Polymers: PVDF and P(VDF-TrFE)

We use first principles methods to study static and dynamical mechanical properties of the ferroelectric polymer Poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoro ethylene (TrFE). We use density functional theory [within the generalized gradient approximation (DFT-GGA)] to calculate structures and energetics for various crystalline phases for PVDF and P(VDF-TrFE). We find that the lowest energy phase for PVDF is a non-polar crystal with a combination of trans (T) and gauche (G) bonds; in the case of the copolymer the role of the extra (bulkier) F atoms is to stabilize T bonds. This leads to the higher crystallinity and piezoelectricity observed experimentally. Using the MSXX first principles-based force field (FF) with molecular dynamics (MD), we find that the energy barrier necessary to nucleate a kink (gauche pairs separated by trans bonds) in an all-T crystal is much lower (14.9 kcal/mol) in P(VDF-TrFE) copolymer than in PVDF (24.8 kcal/mol). This correlates with the observation that the polar phase of the copolymer exhibits a solid-solid a transition to a non-polar phase under heating while PVDF directly melts. We also studied the mobility of an interface between a polar and non-polar phases under uniaxial stress; we find a lower threshold stress and a higher mobility in the copolymer as compared with PVDF. Finally, considering plastic deformation under applied shear, we find that the chains for P(VDF-TrFE) have a very low resistance to sliding, particularly along the chain direction. The atomistic characterization of these "unit mechanisms" provides essential input to mesoscopic or macroscopic models of electro-active polymers.Comment: 15 pages 9 figures Electro-active polyme

Enhancement of polar phases in PVDF by forming PVDF/SiC nanowire composite

Different contents of silicon carbide (SiC) nanowires were mixed with Poly(vinylidene fluoride) (PVDF) to facilitate the polar phase crystallization. It was shown that the annealing temperature and SiC content affected on the phase and crystalline structures of PVDF/SiC samples. Furthermore, the addition of SiC nanowire enhanced the transformation of non-polar α phase to polar phases and increased the relative fraction of β phase in PVDF. Due to the nucleating agent mechanism of SiC nanowires, the ion-dipole interaction between the negatively charged surface of SiC nanowires and the positive CH2 groups in PVDF facilitated the formation of polar phases in PVDF

Piezoelectric and pyroelectric effects of a crystalline polymer

Polyvinylidene flouride (PVDF) is a crystalline polymer to both piezoelectric and pyroelectric nature. Piezoelectricity produces electrical signals when mechanically deformed, and pyroelectricity is the electrical polarization induced by thermal absorption in crystals. To demonstrate the piezoelectric effect PVDF is subjected to impact loads which produce electrical charges proportional to mechanical stresses. A heat source was used to demonstrate the pyroelectric nature of PVDF. The rise in temperature due to absorbed energy by the polymer produces electrical output. The qualitative test results obtained are graphically reproduced

Construction of a Fish-like Robot Based on High Performance Graphene/PVDF Bimorph Actuation Materials.

Smart actuators have many potential applications in various areas, so the development of novel actuation materials, with facile fabricating methods and excellent performances, are still urgent needs. In this work, a novel electromechanical bimorph actuator constituted by a graphene layer and a PVDF layer, is fabricated through a simple yet versatile solution approach. The bimorph actuator can deflect toward the graphene side under electrical stimulus, due to the differences in coefficient of thermal expansion between the two layers and the converse piezoelectric effect and electrostrictive property of the PVDF layer. Under low voltage stimulus, the actuator (length: 20 mm, width: 3 mm) can generate large actuation motion with a maximum deflection of about 14.0 mm within 0.262 s and produce high actuation stress (more than 312.7 MPa/g). The bimorph actuator also can display reversible swing behavior with long cycle life under high frequencies. on this basis, a fish-like robot that can swim at the speed of 5.02 mm/s is designed and demonstrated. The designed graphene-PVDF bimorph actuator exhibits the overall novel performance compared with many other electromechanical avtuators, and may contribute to the practical actuation applications of graphene-based materials at a macro scale

Measurement of Impact Forces on Teeth and Jaw when Wearing Sports Mouth Guards

The objective of this project is to accurately measure the forces the teeth and jaw experience when subjected to impact. For this purpose piezoelectric technology (PVDF), which converts voltage to force and vice versa can be used to measure forces applied to teeth. A PVDF cable is calibrated and used for measuring force along with a control measuring device (PCB Piezotronics). The method involves wrapping the PVDF cable around a 3D home-printed, customized denture. The cable was chosen due to the fact that it allows for adequate fit between mouth guard and denture. Two masses, a baseball and 2 lbs - 3D printed projectile, were dropped from a height of 1m onto the denture with and without mouth guard. Results showed a significant force absorption by the mouth guard (more than 50% of initial impact force). After several trials, (n=10 for each group, baseball with and without mouthguard, as well as 2lbs), it was found that the impact shock absorption by the mouth guard ranged between 60-70%. Figure 1 shows the values at which the denture was impacted, with and without a mouth guard for baseball and 2 lbm cylinder. Finally, FEA Analysis was also used to show the regional stress and strain along the denture.https://scholarscompass.vcu.edu/capstone/1201/thumbnail.jp

Pengaruh Dosis Implantasi Ion Nitrogen pada Sifat Kapasitansi Polimer Pvdf dan Pvdf-hfp

Material berdensitas energi elektrik tinggi sebagai bahan dielektrik kapasitor sangat diperlukan dalam industri bidang elektronika. Tujuan penelitian ini ialah mengkarakterisasi dan menganalisis polimer PVDF( Poly vinylidene fluorde) dan PVDF-HFP (Poly vinylidene fluoride-co-hexafluoropropene) sebelum dan sesudah diimplan ion nitrogen. Metode penelitian yang dilakukan ialah menyiapkan sampel lapisan tipis Polimer PVDFdan PVDF-HFP kemudian diimplan menggunakan ion nitrogen pada dosis 4,69 x 1016 ion/cm2 hingga 1,41 x 1018 ion/cm2 pada energi 10 keV. Selanjutnya nilai kapasitansi, faktor disipasi dan kekuatan dielektrik sampel dikarakterisasi menggunakan LCR meter GW-Instek 800. Morfologi dan ikatan struktur dari sampel dikarakterisasi menggunakan SEM dan FTIR. Hasil percobaan menunjukkan bahwa terjadi peningkatan nilai kapasitansi sebesar 4,3 kali pada polimer PVDF dan 1,4 kali pada polimer PVDF-HPF. Peningkatan nilai kapasitansi disebabkan bertambahnya ikatan rangkap C=C pada PVDF dan PVDF-HFP yang diimplan ion nitrogen. Hal tersebut dibuktikan dari hasil karakterisasi FTIR dan SEM. Namun demikian nilai kekuatan dielektrik mengalami penurunan akibat semakin konduktifnya polimer PVDF dan PVDF-HPF. Untuk sampel PVDF ada kapasitansi optimum dicapai pada dosis 9,38 x 1017 ion/cm2 sedangkan untuk sampel PVDF-HFP diatas dosis tersebut memperlihatkan gejala saturasi. Nilai kapasitansi optimal diperoleh berturut-turut sebesar 0,089483 nF, faktor disipasi 0,129613 % pada polimer PVDF dan 0,134889 nF, faktor disipasi 0,09784 % untuk polimer PVDF-HFP

Pvdf-Tio2 Nanocomposite Membrane with Anti-Fouling Properties for Oil Emulsion Removal

Polivinilidena fluorida (PVDF) membran yang terdedah kepada kotoran emulsi minyak sukar deibersihkan melalui saluran air pada permukaan membran. Sifat hydrophilic titanium dioksida (TiO2) akan mengubah kestabilan larutan polimer semasa fasa penyongsangan dan mengubah morfologi membran. Dalam kajian ini, PVDF-TiO2 membran matriks bercampur yang bersifat pembersihan sinar ultraungu (UV) telah disintesiskan untuk penyingkiran emulsi minyak mentah dalam keadaan kemasinan yang tinggi. Kesan parameter sintesis membran, iaitu kepekatan polimer, jenis pelarut, jenis dan kepekatan TiO2, dan kepekatan polietilena glikol (PEG) telah dikaji. Sifat-sifat fizikokimia membran dinilai dan dikaitkan dengan prestasi dan sifat anti-kotoron membran. Saiz liang dan keporosan membran merupakan kesan mendominasi pengotoran oleh emulsi minyak. Dari segi anti-kotoran, parameter sintesis membran optima diperolehi dengan menggunakan 18 % berat kepekatan polimer dengan menggunakan N,N-dimetilasetamid (DMAc) diguna sebagai pelarut dan ditambah dengan 3 % berat P25 TiO2. Fluks penelapan air yang diperolehi adalah 160.19 ± 11.54 L/m2.hr, penolakan emulsi minyak sebanyak 96.27 ± 0.28 % dengan 23.40 ± 1.10 % nisbah pemulihan fluks (FRR). Ia didapati bahawa tekanan kritikal harus rendah daripada 1.5 bar untuk mengelakkan kotoran di mana rintangan lapisan kek adalah mekanisma utama pengotoran. Selepas 30 min sinaran UV, membrane matriks bercampur menunjukkan peningkatan yang drastik dalam nisbah pemulihan fluks, iaitu sebanyak 90.42 ± 4.90 % di mana ia mengesahkan sifat pembersihan sendiri zarah nano TiO2 dalam mendegredasikan emulsi minyak yang terjerap pada permukaan membran. Namun begitu, penyinaran UV dalam jangka masa yang lebih panjang dan intensiti yang lebih tinggi boleh mengurangkan prestasi membran kerana liang tersumbat disebabkan oleh pemecahan minyak dan pembesaran liang. ________________________________________________________________________________________________________________________ Polyvinylidene fluoride (PVDF) membrane is prone to be fouled by oil emulsions which could not be easily cleaned via surface washing. Besides, hydrophilic nature of titanium dioxide (TiO2) changes the thermodynamic stability of the polymer solution during phase inversion and caused membrane with altered morphology. In this study, PVDF–TiO2 mixed-matrix membranes with UV-cleaning properties were synthesized for crude oil emulsion removal at high salinity condition. The effect of membrane synthesis parameter, namely polymer concentrations, type of solvents, TiO2 type and concentrations, and polyethylene glycol (PEG) concentrations were investigated. The physicochemical properties of the membrane were characterized and related to its performance and antifouling properties. Membrane pore size and porosity were the dominating effects of membrane fouling by oil emulsions. In term of antifouling, the optimum membrane synthesis parameter was obtained by 18 wt.% PVDF with N, Ndimethylacetamide (DMAc) as solvent added with 3 wt.% of P25 TiO2. The obtained pure water permeation flux was 160.19 ± 11.54 L/m2.hr, rejection of 96.27 ± 0.28 % with flux recovery ratio (FRR) of 23.40 ± 1.10 %. It was found that the critical pressure to avoid irreversible fouling should be lower than 1.5 bar whereby cake layer resistance is the main fouling mechanism. Upon 30 min of UV irradiation, the mixedmatrix membrane exhibited drastic FRR improvement of 90.42 ± 4.90 %, which confirms the photocatalytic property of TiO2 nanoparticles in degrading the adsorbed oil emulsions on the membrane surface. Nonetheless, further increased of UV irradiation duration and intensity could deteriorate the membrane performance due to pore blockage caused by the oil fragmentation and pore enlargement